A primer surfacer means a coating agent that is applied in multicoat coatings or multicoat lacquer finishes, e.g. on a primer or a gravel-impact intermediate primer, especially in the motor vehicle sector, and because of its film build evensout the unevennesses of the underlying coat and of the substrate, e.g. of a sheet metal, in order that a smoother surface is produced before the application of the subsequent coats.
Film build accordingly means the capacity of a surface coating to even-out the unevennesses of the substrate, whereby the optical effect of an especially well lacquered surface (build) is produced in the subsequent finishing coat.
The primer surfacer generally contains a higher pigment or extender volume ratio than the subsequent coats. The primer surfacer is achromatic or coloured. It need not match the colour of a subsequent coat.
In the course of time, the primer surfacer will in future have to be as free as possible from organic solvents for ecological reasons. Two approaches to this end are possible: the solvent-based high-solid systems with high solids content and the water-dilutable systems with extremely low content of organic solvents. With the water-dilutable systems, in contrast to the high-solid systems, more interesting primer surfacers with a lower proportion of organic solvents are obtained.
For various reasons, the water-dilutable primer surfacers usable for the automobile industry generally still contain organic solvents. The proportion of these solvents and volatile neutralizing agents must be as small as possible, and as far as possible not more than 25 wt %, preferably not more than 20 wt %, relative to the sum of the percentages by weight of lacquer solids, organic solvents and volatile neutralizing agents; or, in other words, the high-solid value must not be less than 75 wt %, preferably not less than 80 wt %.
The calculation is made according to the formula ##EQU1## FK=g solids (30 minutes at 105.degree. C.) LM=g organic solvents
NM=g volatile neutralizing agents.
There must be no reduction in quality of the lacquering as a result of the replacement of solvent-dilutable primer surfacers by water-dilutable primer surfacers. Up to now, however, a complete adaptation of the properties of water-dilutable primer surfacers with low content of organic solvents has not been achieved to a sufficient degree. Thus in particular the gravel-impact resistance and the corrosion protection are among the properties of water-dilutable primer surfacers that cannot always be obtained reproducibly from batch to batch.
From DE-PS-38 05 629, water-dilutable, gravel-impact-resistant coating agents from combinations of polyesters or acrylate resins with blocked isocyanates are known. An aqueous primer surfacer is applied to these coating agents, so that an additional operation is necessary for the application of the whole lacquer finish.
In the International Patent Application with publication number WO 88/03159, water-dilutable coating agent compositions and aqueous primer surfacers are described that must contain polyesters modified with bisphenol A epoxy resins. The disadvantage of these systems lies in the limited choice of binders. Every expert knows how multifarious and different the requirements for primer surfacers for different applications can be. For this reason, it is necessary not to be restricted to one binder system.